Add Matter Thread Network Diagnostics cluster sensors

[lboue]

Proposed change

• Purpose: Expose Matter Thread Network Diagnostics as Home Assistant sensors to improve troubleshooting and visibility into network stability.
• What’s Added: Three diagnostic sensors from the Thread Network Diagnostics cluster:
  • ThreadNetworkDiagnosticsPartitionId: current Thread network partition ID
  • ThreadNetworkDiagnosticsAttachAttemptCount: attach attempts counter
  • ThreadNetworkDiagnosticsPartitionIdChangeCount: partition ID changes counter

The whole point is to graph them in order to see the changes and thus identify instability.
I would also like to add a Thread network connection reliability indicator on a scale of 1 to 10 in a future PR.

Details

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue: Matter devices become unavailable #159629
• Link to documentation pull request:
• Link to developer documentation pull request:
• Link to frontend pull request:

Checklist

• I understand the code I am submitting and can explain how it works.
• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
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• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.

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• I have reviewed two other open pull requests in this repository.

[home-assistant]

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[Copilot]

Pull request overview

This PR adds three Thread Network Diagnostics cluster sensors to the Matter integration to improve troubleshooting and visibility into Thread network stability for Matter devices:

• Partition ID sensor - Reports the current Thread network partition identifier
• Attach Attempts counter - Tracks cumulative attach attempt count
• Partition ID Changes counter - Tracks how many times the partition ID has changed

All three sensors are diagnostic entities disabled by default to avoid cluttering the UI, following Home Assistant conventions for technical diagnostic data.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

File	Description
homeassistant/components/matter/sensor.py	Adds three MatterDiscoverySchema definitions for Thread Network Diagnostics sensors with appropriate state classes, entity categories, and feature map requirements
homeassistant/components/matter/strings.json	Adds translation keys for the three new sensor entity names
homeassistant/components/matter/icons.json	Assigns antenna icons (mdi:antenna) to all three Thread diagnostic sensors
tests/components/matter/test_sensor.py	Adds comprehensive tests for all three sensors including initial state verification, update handling, entity category validation, and None value handling